The termination of chromosome replication in Escherichia coli will be studied. Prophage lambda reverse and other lambda prophage will be integrated in the terminus region of the chromosome. Induction of excision negative prophage will be used as a means to label radioactively and specifically the adjacent regions of the chromosome. A restriction fragment map of the labeled DNA will then be constructed. The rate and sequence in which the fragments are labeled following prophage induction will be used to determine the length of the terminus region and the properties of the sequences that inhibit replication forks. The rate and sequence in which the fragments are labeled will also be studied in cells that terminate the replication cycle normally. The terminus fragments will be cloned using techniques of recombinant DNA research. A variety of procedures will be tested, since it is anticipated that some of the terminus fragments will be difficult to clone. The terminus fragments will be obtained from F' episomes, or if necessary, from fractionated chromosomal DNA. The nucleotide sequences of the important terminus fragments will be determined. The association between the terminus and the the cell envelope will be studied at different stages of the cell cycle, and in different mutants. Experiments will be conducted to determine if the association is stable or transient. The particular regions of the terminus involved in the association will be characterized.